Test apparatus for pulsed transmitter-receiver systems



June 22, 1954 J. M. WOLF 2,681,986

TEST APPARATUS FOR PULSED TRANSMITTER-RECEIVER SYSTEMS TRANSMITTER Filed Dec. 10, 1945 II I? T.R.BOX

l R.F.

ITTTTTI VIDEO i J INDICATOR INVENTOR JAMES M. WOLF ATTORNEY Patented June 22, 1954 :umreo :"smrns ZTEST APPARATUS F0RZPIJIISEDTTRANS MITTER RECEIVEWSYSTEMS ni'ames'iM; WolffBo'ston, Massmas'signorivbmmesne assignmentauto:theiUnited States of America 1 as represented bmjthe Secretarmofi theNayy "Application. December 10, 1945, Sei'iaFN 0. 634,116

This invention relates totestingdevices, and

"Inthe operation of such systems it is highly desirable to provide a-device capable offurnishing a rapid check of the overall periormanceof "the system. For instance, in-pu1se=echo systems the failureto. locate objects. may not bean indication of trouble'but'may' result" from the ab-' sence ofssuchiobjects .Therefore,- such a testing. device is necessary Ito-indicate a failurenin the system;-as contrasted to-theczlack:of -targets.

-.Certain'types of cavity. resonators, frequently -te1=med.echo boxes, have-been-adaptedta provide an: excellent check of cverallsystem performance. .Such' aresonator is excitedat the carrierxfrenuency. oft-he system bycoupling intouiira small ,.-.portion..of the transmittedgpower.

mitted energy is stored and then reradiated at a sufficiently high power level and for a time sufiiciently long to permit energy so given out to be picked up by the receiver of the system being tested. The period of time for which the energy given out by the resonator can be perceived by the indicating apparatus of the system under test bears a simple relationship to the overall effectiveness of that system. Various methods have been used to couple transmitted power into the resonator, among them being a dipole so placed as to intercept a portion of the power radiated by the systems antenna, and a directional coupler placed in the transmission line connecting the transmitter and the antenna.

The cavity resonator may be replaced by any deivce capable of storing radio energy and then returning this energy to the system. One device so used is an echo line connected to the main transmission line between the receiver and the antenna. By means of a directional coupler, a predetermined portion of the transmitted energy is coupled into the line. If the echo line is terminated in an impedance mismatch at each end, the energy which enters it travels back and forth, being successively reflected from the ends and attenuated exponentially .by the losses in the line. Each time the energy makes a round trip and passes the directional coupler in the proper direction a small fraction of the energy is coupled through the wave selector into the receiver, appearing as a signal on the indicator. The number of echoes appearing on the indicator gives an indication of set efficiency.

In endeavoring to adapt such devices to sys- 1* Glaaim; (CL-250*13) :2: L" temssoperatingsat -very highs carrieritrequencies 'varioius itechhic'al difiiculties becomeipronouneed. -i-Ierett'1fore, all eiiortgas' famas l 'amsawarefihas 1; been: exerted in the idirection or overcoming these diiiiculties by improvingfithe de'sign of suchiebho iiboxes' so as to adapt them -to successtul #:operation at the higher frequencies. I have found that the ?prbblem can be solved by auwhdllyedill'erent approach; inam'ely; by storing: and 'w'reradiaiting the-a energy atthe intermediiite frequencyeoffithe .-.system under -test.

It isi thereiorex the object of thenpresentrinl/611131011 170LprEJVide ai tesfingf devifie "whichircan :be ad apted to use" with systemszoperafingaattany frequency band and which will havezitheesame properties on all bands.

'Thisf-and other objects will bexmorerapparent upon-consideration of the iollowingespecifications, Iitaken-"in connection witli'the accomp anyingi'drawing; the single figure being a blockdiagram -of an embodiment of the invention.

The radio transmission and receiving system shown comprises a transmitter III for generating short-duration high-intensity pulses of high frequency radio energy, a transmission line H, and an antenna l2 for radiating this energy and pickin up any resulting echoes. A receiver 13 is connected to transmission line I I by transmission line I 4, with which is associated a protective electric breakdown device l5. Receiver 13 is broken down into three sections of differing frequency, namely the radio frequency input section, the intermediate frequency section, and the video output section. The output of receiver I3 is connected to indicator I6 which presents the echo indication on a cathode ray tube.

In accordance with the present invention, an echo box I1 is coupled into one of the LE stages of receiver l3. Any convenient type of coupling could be employed, link coupling l8 being shown in the present case. When transmitter in fires, a portion of its output leaks through protective device I 5 and into the receiver. This radio frequency energy is amplified and converted to the intermediate frequency. If echo box I! is resonant at the intermediate frequency, it will store energy during the pulse transmission and reradiate this energy to the system at the conclusion of the pulse. The time during which energy is return to the system, commonly termed ringing time, will be a function of the amount of energy stored during the pulse, the Q of the resonator, and the sensitivity of the receiver. The amount of energy stored during the pulse is a function of the transmitter output power 3 and the gain of the receiver circuits up to the coupling link l8. In order to provide for an extended ringing time, the echo box is so designed that the energy loss per cycle is small previously described, may be usdin place of the resonant echo box.

Since the intermediate frequencies of most'systerns lie within a relatively narrow band, the intermediate frequency echo box or echo line can be adapted to any band and, will have the same properties on all bands. It can be pretuned to the intermediate frequency of the-system, and need .not' be retuned while in use. advantage over operation at the carrier frequency of the system,since the carrier frequency This is a distinct may fluctuategbut automatic frequencycontrol circuits will maintain the intermediate frequency constant.

It is believed that the construction and operation of my invention, as well as the advantages 7 thereof, will be apparent from the foregoing description. It will be understood that while I have-shown and described my invention in a particular embodiment, changes may be made in What is claimed is:

In combination with a system for transmitting and receiving short pulses of radio energy, said system comprising a transmitter for generating short duration, high intensity pulses of high frethecircuits disclosed without departing from the invention.

quency radio energy, a first transmission line connected at one end to the output of said transmitter, an antenna connected at the other end of said transmission line for radiating the generated pulses and for picking up any resulting echoes, a second transmission line, a protective electric breakdown device connected in series with said second transmission line, a receiver, said receiver being connected to said first transmission line through said second transmission line in series with said electrical breakdown device, and an indicator, said indicator'being connected to the output of said receiver, said receiverincluding intermediate frequency circuits, whereby, when said transmitter fires, a portion of its output passes through said protective device into said receiver, an echo box resonant at said intermediate frequency, coupling means between said intermediate frequency circuits and said echo box for coupling a portion of the energy at the intermediate frequencycircuits to said echo box, said echo box storing said portion of energy, said coupling means being the means for transferring some of said stored energy within said echo box back to said intermediate frequency circuits of said receivers, the relative amount of said stored energy which is transferred back to said system being measured by said indicator.

References Cited inthe file of this patent 'UNITED STATES PATENTS Number Name Date 2,041,040 Barden May 19, 1936 2,174,963 Braaten Oct. 3, 1939 2,421,016 Deloraine et al May 2'7, 194'? 2,467,670 Hershberger Apr. 19, 1949 V 2,502,464 Lehmann Apr. 4, 1950 2,510,299 Schramm June 6, 1950 2,532,539

Counter et a1 Dec. 5, 1950 

